Carby Reed Valve on stock Nt carb with billet intake

[DAMIEN1307]

Now that reed intake valving has come into fashion, there will be a lot of “sixth
and seventh” porting done to various engines. There are two different approaches to
adding extra rear-cylinder ports in reed-valve engines: That chosen by Yamaha is simply
to carve a slot leading up from the intake port to link the port cavity with the cylinder
when the piston is down at the bottom of its stroke. This “sixth” port is not fed from the
crankcase; mixture moves up through it and into the cylinder due to the ramming action
of gas inertia in the intake manifold, and also because of the partial vacuum formed in the
cylinder by exhaust system dynamics. Yamaha places the top of this extra transfer ports
on a level with the four already found in their five-port engines, and the roof of the port is
angled upward very sharply - about 70-degrees, in fact. Apparently, such “tuning” as is
done with this kind of port is mostly a matter of varying its width, but not enough
experimental work has been done with it to provide us with any guidelines. The other
approach to this particular kind of transfer port is to cut windows in the rear of the piston
to permit part of the charge compressed in the crankcase to blow up into the intake port,
from where it is then able to escape through the boost port and into the cylinder. From
early reports, the effect of this modification is to improve very substantially an engine's
power range at some expense to peak power. This is, of course, precisely the effect to be
desired in a large-displacement scrambler or motocross engine, but hardly what one
would be looking for from a road racing engine. My own experience with reed valves is
still too limited to permit me any firm conclusions, and the potential benefits of the
porting they make possible, but I am inclined at present to believe that they fall
something short of being the answer to the two-stroke tuner's prayers. Indeed, it may be
that their principal contribution is to keep carburetion clean over a wider speed range than
is possible with piston-controlled intake porting. I very much doubt that reed valving
will ever equal the ordinary piston-controlled induction in terms of maximum horsepower
- though I recognize that reeds have their uses in engines intended for general, all purpose motorcycles.

Nice brick wall of text SR...lol...Every brick is neatly in place...lol...DAMIEN

 

[LewieBike]

I've owned one reed boxed/piston ported bike; a 77 Hodaka Road Toad, which had a very tractable engine for trail riding. Note I said trail riding as I don't ride in races or enduros. The stock RT100 had a very useable spread of RPM while also being able to rev very freely. From what I gather it had two transfer ports with a small boost off the reedbox. I consider it and the old Suzuki TS90 rotary valve as two of the better small displacement 2 cycle trailbikes from the 1970's.

 

[Karl Snarl]

I've owned one reed boxed/piston ported bike; a 77 Hodaka Road Toad, which had a very tractable engine for trail riding. Note I said trail riding as I don't ride in races or enduros. The stock RT100 had a very useable spread of RPM while also being able to rev very freely. From what I gather it had two transfer ports with a small boost off the reedbox. I consider it and the old Suzuki TS90 rotary valve as two of the better small displacement 2 cycle trailbikes from the 1970's.

Thats what im debating to do. A small boost port. God of smokers books taught me how to use the boost port for what ever tuning. The small one i am debating is for low end. Has no effect at higher rpms. I only built one screamer, didnt like it. Not very trail or street friendly.

 

[LewieBike]

My only regret is not owning more 2 stroke DS bikes. I have owned through luck and chance far too many Honda 90 Trail bikes. That little transfer box on the transmission was just too useful. Otherwise that engine on the Honda Trail is the most boring thing ever bolted to a bike.

 

[Karl Snarl]

My only regret is not owning more 2 stroke DS bikes. I have owned through luck and chance far too many Honda 90 Trail bikes. That little transfer box on the transmission was just too useful. Otherwise that engine on the Honda Trail is the most boring thing ever bolted to a bike.

Lol, most boring thing.... It aint to late to start buying more 2t. Ive loved 'em since i could sit on a little 50cc. Had buddies that raced motocross, used to help in the pit and garage. Learned a lot from those rough old men, when i was a kid. Even had a buddy that his grandpa did jet dragsters and worked for lockheed. Now there is some power. Lets do that to a bike. Lol jk.

 

[LewieBike]

Thats what im debating to do. A small boost port. God of smokers books taught me how to use the boost port for what ever tuning. The small one i am debating is for low end. Has no effect at higher rpms. I only built one screamer, didnt like it. Not very trail or street friendly.

That's my only complaint about my 48 cc HT engine, it's just a little too soft on power below 9 mph with stock gearing. Funny because it idles fine and will seem to rev willingly without bogging with the clutch disengaged.

 

[DAMIEN1307]

Even had a buddy that his grandpa did jet dragsters and worked for lockheed. Now there is some power. Lets do that to a bike. Lol jk.

Be careful what you ask for, you just might get it...lol...DAMIEN

 

[LewieBike]

Lol, most boring thing.... It aint to late to start buying more 2t. Ive loved 'em since i could sit on a little 50cc. Had buddies that raced motocross, used to help in the pit and garage. Learned a lot from those rough old men, when i was a kid. Even had a buddy that his grandpa did jet dragsters and worked for lockheed. Now there is some power. Lets do that to a bike. Lol jk.

I have in the past owned a pair of Yamaha trail bikes, a L5T-A 100cc and the 68 YG5-T but they were in rough shape. Just not enough inclination to do much with them. The LT5-A I owned before the PO had swapped in a rare YA6 125 into. It was memorable for the amount of torque it could pour on, just didn't have the ability to spin beyond 6K easily.

 

[LewieBike]

Be careful what you ask for, you just might get it...lol...DAMIEN

I'm waiting for someone to mount a RC helicopter turbine engine to a bike. There's big difference between moving a big column of hot air out the back and harnessing that +120K rpm to turn wheels.

 

[Karl Snarl]

I'm waiting for someone to mount a RC helicopter turbine engine to a bike. There's big difference between moving a big column of hot air out the back and harnessing that +120K rpm to turn wheels.

Russians did it. I just seen it the other night. Giant helicopter turbine on a custom trike like build. They pulled the engine from the bottom of a river. An these guys bought it for 200 bucks and rebuilt it. No knowledge of them engines at all, till they tore it apart. Lol.

Oh wait you said rc. Lol. These guys used a real helo turbine.